Blades comprised in propellers and fans usually work under severe conditions. The design parameters and security margins are carefully set, but it is not impossible that a blade may break and release from the hub. In this case, the blade may impact on other blades or on other parts of the aircraft, causing some damage to them.
Some aircraft are powered by engines which comprise unducted propeller blades. These engines are joined to the aircraft structure by pylons. They can be located in the wing section, under a high wing for example, or on the rear end of the fuselage. In the latter case, the pylons which support these engines are usually not very long, so the engines and thus the propeller blades are located in close proximity to the fuselage structure. A blade release or rupture can therefore be critical in these cases, as it can cause damage to the fuselage structure or even to the opposite engine.
The solutions proposed in the state of the art include the reinforcement of the fuselage in the parts that are predictably impacted by a blade which is released from a propeller. However, this solution pose a weight increase in the aircraft structure and a not very secure position, as a released blade at high speed may draw a not very predictable trajectory. Weight is a critical issue in aircraft design, so this drawback is very important in this technical field.